From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.2 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A40DAC433E9 for ; Thu, 21 Jan 2021 19:13:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 73C4723A53 for ; Thu, 21 Jan 2021 19:13:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726997AbhAUTMu (ORCPT ); Thu, 21 Jan 2021 14:12:50 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56940 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727001AbhAUTK4 (ORCPT ); Thu, 21 Jan 2021 14:10:56 -0500 Received: from fieldses.org (fieldses.org [IPv6:2600:3c00:e000:2f7::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4A1C8C061756; Thu, 21 Jan 2021 11:09:38 -0800 (PST) Received: by fieldses.org (Postfix, from userid 2815) id 7790068A6; Thu, 21 Jan 2021 14:09:37 -0500 (EST) DKIM-Filter: OpenDKIM Filter v2.11.0 fieldses.org 7790068A6 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=fieldses.org; s=default; t=1611256177; bh=N/byAs1v6tc9Fx3ki4Hix9OpQ2b4N7bUlr5L+Udyz04=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=v12SGAI5TdTGVdUXLNRFq4bYEJiB3wwXNox11gArFVnndbZSQLf36kKRFo95UyeQY CO7QjlprxG0AHzpbsAXIme2ZNIcWn0te5LWMp6nGA+4cNMBpacJ9xmATTjhLCoftDm vFchlftsuiau3nyD/mo1dMyfCGV87yqk3pnkw+U0= Date: Thu, 21 Jan 2021 14:09:37 -0500 From: "J. Bruce Fields" To: David Howells Cc: Trond Myklebust , Anna Schumaker , Steve French , Dominique Martinet , Takashi Iwai , Matthew Wilcox , linux-afs@lists.infradead.org, Jeff Layton , David Wysochanski , Alexander Viro , linux-cachefs@redhat.com, linux-nfs@vger.kernel.org, linux-cifs@vger.kernel.org, ceph-devel@vger.kernel.org, v9fs-developer@lists.sourceforge.net, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC][PATCH 00/25] Network fs helper library & fscache kiocb API Message-ID: <20210121190937.GE20964@fieldses.org> References: <20210121174306.GB20964@fieldses.org> <20210121164645.GA20964@fieldses.org> <161118128472.1232039.11746799833066425131.stgit@warthog.procyon.org.uk> <1794286.1611248577@warthog.procyon.org.uk> <1851804.1611255313@warthog.procyon.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1851804.1611255313@warthog.procyon.org.uk> User-Agent: Mutt/1.5.21 (2010-09-15) Precedence: bulk List-ID: X-Mailing-List: linux-nfs@vger.kernel.org On Thu, Jan 21, 2021 at 06:55:13PM +0000, David Howells wrote: > J. Bruce Fields wrote: > > > > Fixing this requires a much bigger overhaul of cachefiles than this patchset > > > performs. > > > > That sounds like "sometimes you may get file corruption and there's > > nothing you can do about it". But I know people actually use fscache, > > so it must be reliable at least for some use cases. > > Yes. That's true for the upstream code because that uses bmap. Sorry, when you say "that's true", what part are you referring to? > I'm switching > to use SEEK_HOLE/SEEK_DATA to get rid of the bmap usage, but it doesn't change > the issue. > > > Is it that those "bridging" blocks only show up in certain corner cases > > that users can arrange to avoid? Or that it's OK as long as you use > > certain specific file systems whose behavior goes beyond what's > > technically required by the bamp or seek interfaces? > > That's a question for the xfs, ext4 and btrfs maintainers, and may vary > between kernel versions and fsck or filesystem packing utility versions. So, I'm still confused: there must be some case where we know fscache actually works reliably and doesn't corrupt your data, right? --b.